1. Field of the Invention
The present invention relates to a semiconductor device and a method for producing the same, and an anisotropic conductive circuit board. In particular, the present invention relates to a semiconductor device employing a circuit board including a bonding pad portion on which a semiconductor element is to be mounted on its upper surface and electrode pads connected to electrode terminals of the semiconductor element via a connecting member, and a method for producing such a semiconductor device, and relates to a semiconductor device having good electrical and thermal characteristics and a method for producing such a semiconductor device.
2. Description of Related Art
Hereinafter, a semiconductor device employing a commonly used printed circuit board used as a component of a semiconductor package will be described.
FIGS. 8A to 8E are views illustrating the production process of a conventional LGA (lard grid array) type semiconductor device in the order of the production. FIG. 8A is a plan view, FIGS. 8B to 8E are cross-sectional views of a relevant part taken along line A-A1 of FIG. 8A.
First, to produce a printed circuit board as shown in FIG. 8A, an insulating substrate 2 to which copper foils having a thickness of 6 to 35 xcexcm are attached to its upper and lower surfaces is prepared. This insulating substrate 2 is a substrate in which glass fabrics have been incorporated into an epoxy resin.
Next, via holes are formed having a predetermine diameter in predetermined positions of the insulating substrate with a drill or a laser. Then, thick copper films are formed on the side walls of the formed via holes by electroless plating or electrolytic plating. At this point, the copper foils on the upper and the lower surfaces of the insulating substrate are connected by the thick copper films.
Next, dry films are attached onto the surfaces of the copper foils on the upper and the lower surfaces of the insulating substrate by heating and pressing. The dry films are made of a material that causes a reaction with respect to light having a specific wavelength, and the surfaces of the dry films are irradiated with light having a wavelength for a reaction via a photomask on which a predetermined circuit pattern has been formed. Thereafter, in the circuit pattern formed on the dry films on the copper foil surface on the upper and the lower surfaces of the insulating substrate, the portions to be removed of the dry films are dissolved with a developer and removed after exposure to the light. Then, after the removal, the dry films are heated or irradiated with ultraviolet rays so that the remaining portions of the dry films are cured. Using these dry films as masks, exposed copper film portion is removed by allowing the copper foil erosion chemicals such as nitric acid, sulfuric acid or hydrochloric acid to be in contact with the surface of the copper foils, for example, by dipping or spraying.
Finally, the dry films that have been exposed to the chemicals and cured are removed by using a detaching agent, dissolving it in oxygen plasma, or converting it to carbon dioxide. Solder resist films are formed on the upper and the lower surfaces of the thus obtained printed circuit board 1 by screen printing, and the pattern is formed on the solder resist film via a photomask by an exposure machine. Then, the portion to be dissolved of the solder resist film is dissolved with a developer and removed, and then heated and cured. Then, nickel and gold are deposited in this order in predetermined thicknesses by electrolytic plating on the surface of the copper foil portion corresponding to the opening of the pattern from which the solder resist film is removed. Thereafter, the printed circuit board is divided so as to form a frame shape or divided into individual segments by stamping with a pressing machine or a cutting machine.
The printed circuit board 1 for use in a conventional board structure package, which includes bonding pads, electrode pads, and through-holes connecting the bonding pads and the electrode pads on the upper surface to those on the lower surface, has been produced in this manner.
As shown in FIG. 8A, on each of the upper and the lower surfaces of the insulating substrate 2, the produced printed circuit board 1 includes a bonding pad 3, electrode pads 4 and through-holes 6 connecting the pads 3 and 4 on the upper surface to the corresponding pads on the lower surface. The surface of each of the pads on the printed circuit board 1 is coated with a thin film made of gold or silver. The bonding pad 3 consists of the upper bonding pad and the lower bonding pad, and the electrode pad 4 consists of the upper electrode pad and the lower electrode pad. A solder resist film 5 is formed on the substrate in such a manner that the pads 3 and 4 are exposed.
Next, referring to 8A to 8E, a method for producing a semiconductor device (for a LGA type package) including the printed circuit board 1 will be described below.
First, the circuit board 1 as shown in FIG. 8A is prepared. In the prepared circuit board 1, as shown in FIG. 8B, an upper bonding pad 3a, a lower bonding pad 3b, upper electrode pads 4a, and lower electrode pads 4b are formed on an insulating substrate 2, and through-holes 6 for connecting the bonding pads 3a and 3b and the electrode pads 4a and 4b on the upper surface of the substrate to the corresponding pads on the lower surface are provided.
Then, as shown in FIG. 8C, a die bonding process is performed, in which a semiconductor element 7 is attached onto the upper bonding pad 3a with a conductive adhesive 8 such as silver paste, and then heating is performed at 150xc2x0 C. for one hour in the air for strong adhesion.
Then, as shown in FIG. 8D, a wire bonding process is performed, in which electrode terminals (not shown) on the semiconductor element 7 mounted on the substrate are connected to the upper electrode pads 4a with connecting members 9 such as metal fine lines (wires) using a wire bonder. This connection is performed under the following conditions: The heating temperature of the printed circuit board 1 is 200xc2x0 C., the load for connection between the connecting members 9 and the electrode terminals of the semiconductor element 7 is 20 gf, and the load for connection between the connecting members 9 and the upper electrode pads 4a on the printed circuit board 1 is 100 gf. This connection is performed using ultrasonic vibration as well.
Next, as shown in FIG. 8E, an outline molding process is performed, in which a sealing resin 10 is molded to a predetermined package outline with a transfer mold or a print sealing so that the semiconductor element 7 and the connecting members 9 provided on the upper surface of the printed circuit board 1 are sealed and formed into one piece.
In this manner, a semiconductor device for an LGA type package including a conventionally commonly used printed circuit board as a component is produced. Furthermore, if metal ball terminals are provided on the lower electrode pads 4b (land portions) on the bottom surface of the printed circuit board 1, a BGA (ball grid array) type semiconductor package can be achieved.
However, the conventional semiconductor device has the following problems. In the conventional printed circuit board type package including a glass epoxy substrate, the connection between the upper electrode pads and the lower electrode pads or the connection between the upper bonding pad and the lower bonding pad are established via the via holes, so that variations in the structure of the via holes or the plating thickness in the via holes may cause variations in the electrical resistance or the inductance of the wiring portions. Furthermore, since the substrate material is an organic substance, a dielectric constant of the printed circuit board is large, so that it is not suitable to a semiconductor package that requires a high frequency performance. In addition to this problem, there is also an electricity and moisture resistance-related problem in that a water content enters the inside from the outside via the via holes and corrodes the copper foil layer in the upper electrode pad portion of the printed circuit board to which the connecting members such as wire are connected.
Furthermore, the printed circuit board is made of glass epoxy, so that this is insulative with respect to thermal conduction. This causes a heat-related problem as well. More specifically, when a semiconductor element having high power consumption is mounted on the printed circuit board, heat is not released sufficiently, so that the temperature increases in the principal surface on which an integrated circuit is formed in the semiconductor element. As a result, the temperature in the principal surface exceeds the allowable temperature, which leads to malfunction of the circuit.
Therefore, with the foregoing in mind, it is a main object of the present invention to provide a semiconductor device employing a circuit board that has good electrical and thermal characteristics and a method for producing such a semiconductor device.
A semiconductor device of the present invention includes a circuit board; a semiconductor element that is mounted on an upper surface of the circuit board and has an electrode terminal; and a sealing resin for sealing a periphery of the semiconductor element that is mounted on the upper surface of the circuit board. The circuit board includes a plurality of conductive members and an insulating substance for binding and fixing the plurality of conductive members to each other. Each of the plurality of conductive members includes a conductive material formed integrally from the upper surface through the lower surface of the circuit board, and an insulating material covering an outer circumference of the conductive material. The conductive material of at least one conductive member of the plurality of conductive members is exposed to the upper surface of the circuit board. The electrode terminal of the semiconductor element is electrically connected to the conductive material of the conductive member exposed to the upper surface of the circuit board via a connecting member.
In one embodiment of the present invention, a bonding pad made of a metal coating film connected to the conductive material of a part of the plurality of conductive members, and an electrode pad connected to the conductive material of a part of the plurality of conductive members are provided on the upper surface of the circuit board. The semiconductor element is mounted on the bonding pad. The electrode terminal of the semiconductor element is connected to the electrode pad via the connecting member. A lower electrode pad corresponding to the electrode pad on the upper surface is provided on a lower surface of the circuit board. The lower electrode pad is connected to the conductive material of the conductive member connected to the electrode pad provided on the upper surface.
It is preferable that the conductive material of at least one conductive member of the plurality of conductive members is exposed to the lower surface of the circuit board, and a ball electrode or a protruding electrode is connected to the conductive material of the conductive member exposed to the lower surface of the circuit board.
In one embodiment of the present invention, the conductive material is a fine line-like conductive material.
In one embodiment of the present invention, the conductive material has a cross-sectional shape of a circle or a polygon.
In one embodiment of the present invention, the conductive member and the insulating substance are exposed alternately to a side surface of the circuit board.
It is preferable that the circuit board is an anisotropic conductive circuit board that has electrical conductivity with respect to the upper and the lower surfaces and is electrically insulated in a horizontal direction.
In one embodiment of the present invention, a shape of the circuit board viewed from the upper surface thereof is any one of a circle, a rectangle, a hexagon and an octagon.
In one embodiment of the present invention, the connecting member is a conductive metal fine line or a metal ribbon.
In one embodiment of the present invention, the connecting member is a conductive protruding electrode.
A method for producing a semiconductor device of the present invention includes the steps of: (a) bundling and arranging a plurality of conductive members, each of which includes fine line-like conductive materials whose outer circumference is covered with an insulating material to form a conductive member cluster; (b) attaching and fixing the conductive members constituting the conductive member cluster to each other with an insulative resin to form a rectangular solid substrate block; (c) slicing the substrate block with a predetermined thickness to form a substrate element in which cross-sections of the plurality of conductive materials and the insulating materials covering the outer circumferences of the corresponding conductive materials are arranged and whose periphery is made of the insulating resin and the plurality of conductive members; (d) forming metal coating films on an upper surface and a lower surface of the substrate element, thereby forming a circuit board; (e) mounting a semiconductor element having an electrode terminal on an upper surface of the circuit board; (f) electrically connecting the electrode terminal of the semiconductor element mounted on the circuit board and the conductive material positioned on the upper substrate of the circuit board with a connecting member; and (g) sealing a periphery of the semiconductor element mounted on the upper surface of the circuit board and the connecting member with a sealing resin.
In one embodiment of the present invention, in the step (C), slicing is performed at an angle between 30xc2x0 to 150xc2x0 with respect to the longitudinal direction of the conductive member cluster constituting the substrate block such that a thickness becomes 0.05 mm to 3.00 mm.
It is preferable that the method for producing a semiconductor device further includes performing surface-processing by polishing both surfaces of the sliced substrate element, after the step (c).
In one embodiment of the present invention, the step (d) includes forming a metal coating film in a portion on the upper surface of the substrate element on which the semiconductor element is to be mounted to form a bonding pad portion; forming a metal coating film as an electrode pad connected to the conductive material of the substrate element in a portion of the upper surface of the substrate element to which a connecting member for electrically connecting to the electrode terminal of the semiconductor element to be mounted is to be connected, and forming a metal coating film on the conductive material exposed on the lower surface of the substrate element to form an electrode pad.
It is preferable that in the step (a), a plurality of conductive members are bundled and arranged in a plurality of rows such that they are densely filled in a grid or staggered manner in cross-section.
In one embodiment of the present invention, in the step (f), the connection is performed using a conductive metal fine line as the connecting member.
In one embodiment of the present invention, in the step (f), the connection is performed using a conductive protruding electrode as the connecting member.
In one embodiment of the present invention, the method for producing a semiconductor device further includes forming a ball electrode or a protruding electrode on an electrode pad on the conductive material exposed on the lower surface of the circuit board, after the step (g).
In one embodiment of the present invention, in the step (a), the conductive material is a metal fine line made of at least one selected from the group consisting of copper, a copper alloy, aluminum, an aluminum alloy, nickel, and a nickel alloy.
A circuit board of the present invention includes a plurality of conductive member; an insulating substance for binding and fixing the plurality of conductive members to each other; wherein each of the plurality of conductive members include a conductive material formed integrally from one end through the other end and an insulating material for covering an outer circumference of the conductive material, and there is a difference in conductivity between a direction to which the conductive material extends and directions other than that.
According to the present invention, a semiconductor element is mounted on the upper surface of a circuit board obtained by binding and fixing a plurality of conductive members, each of which includes a conductive material formed integrally from the upper surface through the lower surface of the circuit board, using an insulative substance. Therefore, the electrical resistance and the inductance between the upper and the lower surfaces of the board are significantly small, so that an electrically and thermally excellent semiconductor device can be achieved.